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mapper_cbs.go
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mapper_cbs.go
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// This file is part of Gopher2600.
//
// Gopher2600 is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Gopher2600 is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Gopher2600. If not, see <https://www.gnu.org/licenses/>.
package cartridge
import (
"fmt"
"math/rand"
"github.com/jetsetilly/gopher2600/curated"
"github.com/jetsetilly/gopher2600/hardware/memory/bus"
"github.com/jetsetilly/gopher2600/hardware/memory/cartridge/mapper"
"github.com/jetsetilly/gopher2600/hardware/memory/memorymap"
)
// from bankswitch_sizes.txt:
//
// 12K:
//
// -FA: Used only by CBS. Similar to F8, except you have three 4K banks
// instead of two. You select the desired bank via 1FF8, 1FF9, and 1FFA.
// These carts also have 256 bytes of RAM mapped in at 1000-11FF. 1000-10FF
// is the write port while 1100-11FF is the read port.
//
//
// cartridges:
// - Omega Race
// - Gorf
type cbs struct {
mappingID string
description string
// cbs cartridges have 3 banks of 4096 bytes
bankSize int
banks [][]uint8
// rewindable state
state *cbsState
}
func newCBS(data []byte) (mapper.CartMapper, error) {
cart := &cbs{
mappingID: "FA",
description: "CBS",
bankSize: 4096,
state: newCbsState(),
}
if len(data) != cart.bankSize*cart.NumBanks() {
return nil, curated.Errorf("FA: %v", "wrong number of bytes in the cartridge data")
}
cart.banks = make([][]uint8, cart.NumBanks())
for k := 0; k < cart.NumBanks(); k++ {
cart.banks[k] = make([]uint8, cart.bankSize)
offset := k * cart.bankSize
copy(cart.banks[k], data[offset:offset+cart.bankSize])
}
return cart, nil
}
// Mapping implements the mapper.CartMapper interface.
func (cart *cbs) Mapping() string {
return fmt.Sprintf("Bank: %d", cart.state.bank)
}
// ID implements the mapper.CartMapper interface.
func (cart *cbs) ID() string {
return cart.mappingID
}
// Snapshot implements the mapper.CartMapper interface.
func (cart *cbs) Snapshot() mapper.CartMapper {
n := *cart
n.state = cart.state.Snapshot()
return &n
}
// Plumb implements the mapper.CartMapper interface.
func (cart *cbs) Plumb() {
}
// Reset implements the cartMapper interface.
func (cart *cbs) Reset(randSrc *rand.Rand) {
for i := range cart.state.ram {
if randSrc != nil {
cart.state.ram[i] = uint8(randSrc.Intn(0xff))
} else {
cart.state.ram[i] = 0
}
}
cart.state.bank = len(cart.banks) - 1
}
// Read implements the mapper.CartMapper interface.
func (cart *cbs) Read(addr uint16, passive bool) (uint8, error) {
if addr >= 0x0100 && addr <= 0x01ff {
return cart.state.ram[addr-0x100], nil
}
cart.bankswitch(addr, passive)
return cart.banks[cart.state.bank][addr], nil
}
// Write implements the mapper.CartMapper interface.
func (cart *cbs) Write(addr uint16, data uint8, passive bool, poke bool) error {
if cart.bankswitch(addr, passive) {
return nil
}
if addr <= 0x00ff {
cart.state.ram[addr] = data
return nil
}
if poke {
cart.banks[cart.state.bank][addr] = data
return nil
}
return curated.Errorf("FA: %v", curated.Errorf(bus.AddressError, addr))
}
// bankswitch on hotspot access.
func (cart *cbs) bankswitch(addr uint16, passive bool) bool {
if addr >= 0x0ff8 && addr <= 0xffa {
if passive {
return true
}
if addr == 0x0ff8 {
cart.state.bank = 0
} else if addr == 0x0ff9 {
cart.state.bank = 1
} else if addr == 0x0ffa {
cart.state.bank = 2
}
return true
}
return false
}
// NumBanks implements the mapper.CartMapper interface.
func (cart *cbs) NumBanks() int {
return 3
}
// GetBank implements the mapper.CartMapper interface.
func (cart *cbs) GetBank(addr uint16) mapper.BankInfo {
// cbs cartridges are like atari cartridges in that the entire address
// space points to the selected bank
return mapper.BankInfo{Number: cart.state.bank, IsRAM: addr <= 0x00ff}
}
// Patch implements the mapper.CartMapper interface.
func (cart *cbs) Patch(offset int, data uint8) error {
if offset >= cart.bankSize*len(cart.banks) {
return curated.Errorf("FA: %v", fmt.Errorf("patch offset too high (%v)", offset))
}
bank := offset / cart.bankSize
offset %= cart.bankSize
cart.banks[bank][offset] = data
return nil
}
// Listen implements the mapper.CartMapper interface.
func (cart *cbs) Listen(_ uint16, _ uint8) {
}
// Step implements the mapper.CartMapper interface.
func (cart *cbs) Step(_ float32) {
}
// GetRAM implements the mapper.CartRAMBus interface.
func (cart *cbs) GetRAM() []mapper.CartRAM {
r := make([]mapper.CartRAM, 1)
r[0] = mapper.CartRAM{
Label: "CBS+RAM",
Origin: 0x1080,
Data: make([]uint8, len(cart.state.ram)),
Mapped: true,
}
copy(r[0].Data, cart.state.ram)
return r
}
// PutRAM implements the mapper.CartRAMBus interface.
func (cart *cbs) PutRAM(_ int, idx int, data uint8) {
cart.state.ram[idx] = data
}
// IterateBank implements the mapper.CartMapper interface.
func (cart *cbs) CopyBanks() []mapper.BankContent {
c := make([]mapper.BankContent, len(cart.banks))
for b := 0; b < len(cart.banks); b++ {
c[b] = mapper.BankContent{Number: b,
Data: cart.banks[b],
Origins: []uint16{memorymap.OriginCart},
}
}
return c
}
// ReadHotspots implements the mapper.CartHotspotsBus interface.
func (cart *cbs) ReadHotspots() map[uint16]mapper.CartHotspotInfo {
return map[uint16]mapper.CartHotspotInfo{
0x1ff8: {Symbol: "BANK0", Action: mapper.HotspotBankSwitch},
0x1ff9: {Symbol: "BANK1", Action: mapper.HotspotBankSwitch},
0x1ffa: {Symbol: "BANK2", Action: mapper.HotspotBankSwitch},
}
}
// WriteHotspots implements the mapper.CartHotspotsBus interface.
func (cart *cbs) WriteHotspots() map[uint16]mapper.CartHotspotInfo {
return cart.ReadHotspots()
}
// rewindable state for the CBS cartridge.
type cbsState struct {
// identifies the currently selected bank
bank int
// some atari ROMs support aditional RAM. this is sometimes referred to as
// the superchip. ram is only added when it is detected
ram []uint8
}
func newCbsState() *cbsState {
const cbsRAMsize = 256
return &cbsState{
ram: make([]uint8, cbsRAMsize),
}
}
// Snapshot implements the mapper.CartMapper interface.
func (s *cbsState) Snapshot() *cbsState {
n := *s
n.ram = make([]uint8, len(s.ram))
copy(n.ram, s.ram)
return &n
}